The invention concerns a drill which is equipped with a frame and with furrow opening knife hoes which are movable in a vertical plane and disposed on shanks, and which have each two laterally projecting wings bent downwardly in the manner of an inverted V, with their outer edges merging forwardly with one another, and which have in their center an upright strut.
A seed drill of this kind is already disclosed in Swedish Pat. No. 359,721. In this drill, the shanks of the hoes are disposed on the frame for pivoting about horizontal axes in a vertical plane, while each of the upright struts fastened to the hoe shanks and to the openers has an edge extending forwardly and upwardly at an angle from the tip of the knife hoe. By means of this cutting edge, the knife hoes engaging the ground in operation are lifted if they collide with an obstruction in the soil, thereby preventing damage to these hoes and their shanks. It is furthermore advantageous that the seeds are placed in the soil in a broader swath by each knife hoe, resulting a greater stability of the individual plants in the soil after germination of the seed, and this can result in greater yields. It is a considerable disadvantage in this drill, however, that the depth of penetration of the knife hoes into the soil cannot be maintained constant. This deficiency is to be attributed to the fact that the attitude angle of the wings of the hoes varies upon the slightest rocking movement of the shanks. On this account, the knife hoes perform upward and downward movements in the soil, even in the case of small differences in the consistency of the soil which are always present in practice. Differences in the depth at which the seeds are deposited in the soil, however, result in different germination times for the individual seeds, which can contribute to smaller yields. These differences of depth of penetration of the knife hoes into the soil are further increased by the fact that the hoes penetrate considerably deeper into looser soils than they do into denser soils.
Furthermore, another important disadvantage of this drill is that it can be used only on fields well prepared for seeding. However, it has been found advantageous in agricultural practice, for the maintenance of the capillarity of the soil, biological equilibrium and the natural formation of humus associated therewith, and with regard to the saving of labor, to plant the seeds in the soil without preparatory plowing, i.e., without turning over the upper layers of the soil. Now, if, in the practice of this method of "no-till" cultivation of the soil with the known machine, the attitude angle of the wings of the knife hoes is made great enough to assure the entry of the hoes into unprepared soils, the hoes, after penetrating the surface of the ground covered with stubble and vegetation, will penetrate so deeply into the soil that on lighter soils the seeds can easily become buried too deep. On heavier soils, however, in which the furrows produced by the hoes will not close up again even partially by themselves behind the hoes, wide furrows will be formed, which also will fail to be smoothed over by the press wheels installed behind the hoes on the known drill, so that most of the seeds will lie uncovered on the soil. This will then produce the danger of the waterlogging or the desiccation of the soil, depending on weather conditions, which in turn can cause great losses of germination and hence crop losses.
If, however, the attitude angle of the hoe wings is so low that the above-named difficulties are largely overcome, the hoes will ride on top of the surface layer of vegetation and stubble without penetrating into the soil. The seeds will thus be deposited on the surface rather than in the soil, resulting again in the same losses of germination and crop losses. The forwardly slanting front edge of the upright struts on the hoes produces a disadvantageous effect to the extent that pieces of vegetation and stubble gather under it and additionally impair the penetration of the hoes into the soil.
A drill is furthermore disclosed by British Pat. No. 873,737, which is equipped with conventional furrow openers which are carried each by a parallel guiding means on the frame of the machine. This results in the advantage that the attitude angle of the openers with respect to the soil is maintained at all depths of penetration. Furthermore, to keep the depth of penetration constant, a runner is disposed on each furrow opener.
It is disadvantageous in this drill that the seeds are deposited in only narrow furrows in the soil, resulting in lower yields than in the swath planting method. Furthermore, this drill can be used only on fields that are well prepared for seeding, i.e., plowed and harrowed, because conventional furrow openers are not capable of penetrating unworked soils covered with vegetation and stubble. Also, the runners additionally prevent the penetration of the openers into the soil, because the vegetation and stubble gather under them so that the furrow openers ride above the surface of the soil.